In a radio signal processing, a filtering processing is used for eliminating unwanted components included in signals having an interference potential, spurious, or the like. Although circuits performing the filtering processing include analog filter circuits using analog circuits and digital filter circuits using digital circuits, in recent years, use of the digital filter circuits has become frequent. This is because digital circuits make it possible for the filtering processing to be performed with a high degree of accuracy and at a low cost.
There exists a digital rate conversion filter as a type of digital filter. The digital rate conversion filter adjusts a sampling rate such as a digitized intermediate frequency signal (IF signal) and a baseband signal, and at the same time, is used for the purposes of eliminating spurious signals, preventing aliasing or the like. A decimation filter is used for decreasing the sampling rate so that it is less than that parent signals. An interpolation filter is used for increasing the sampling rate so that it is more than that of parent signals.
Like the above digital rate conversion filter, configurations connecting FIR (Finite Impulse Response) in series filters and multiple-stage are much used when, for example, a rate ratio of input data and output data is high.
For instance, Patent Literature 1 discloses a multi-stage filter processing device that includes 1/24 of a decimation filter composed of 1/12 of a decimation filter in combination with ½ of a decimation filter. Further, Patent Literature 2 discloses another multi-stage filter processing device that includes 1/64 of a decimation filter composed of 1/16 of a decimation filter in combination with ¼ of a decimation filter.
Furthermore, Patent Literature 3 to 6 disclose multi-stage filter processing devices.